When we dive at depth the pressure increases. This has significant consequences that we must consider and take steps to avoid adverse and unwanted consequences. In addition to arterial gas embolisms, pressure can also cause the bends or decompression sickness (DCI). To understand how this works, we need to consider the gas we are breathing. The most common gas a diver will use is air, which it made up of 21% oxygen and 79% nitrogen. As we dive this mix is delivered via the second stage regulator at the ambient pressure or ATM. So if we are at 10 meters the ATM is 2 and if at 20 meters ATM is 3 and so on. This means that the components of the gas we are breathing at the specified depth is increased by that factor of the ATM so at 20 meters we are breathing in 3 times more nitrogen.
How to avoid the bends?
Our blood collects this extra nitrogen and bubbles start to form. This will continue the longer and deeper we go. This is where our no decompression limit (NDL) comes into play. When our body passes the theoretical threshold of the maximum amount of nitrogen that we can endure our NDL reaches zero. If you exceed your NDL you are now diving in the equivalent of an overhead environment, in that even if you wanted to, you cant go straight to the surface. If you did you would probably suffer decompression sickness, which you really don’t want. At worst you can end up dead or confined to a wheelchair for the rest of your life. This is why dive computers are so important as they use advanced algorithms that will calculate this for you. Even if you maintain your NDL you can still suffer from the bends for two reasons, one your ascent rate was too fast or some other physiological factor such as being overweight or sick.
You ascent rate is important as it gives you body a chance to off-gas the nitrogen as you ascend and the pressure decreases. If you ascend too fast the nitrogen will form bubbles in your tissues and bloodstream. To prevent this from happening all you have to do is maintain a slow ascent to the surface, the slower the better. I have a habit of deploying my surface marker buoy at depth and then reeling up slowly to achieve this.
Like most activities, your general health will play a factor on safety. If you smoke, are overweight, sick or on medication they can all influence the effects of DCI or other diving related injuries. The most important thing to do is to always try and be healthy and don’t go diving if you are out of shape.